In general, a mat is made from a proper material or in a proper shape for softly supporting the buttock portion of a user when the user sits on the floor but not for the purpose of keeping the physiological curvature of the backbone.
Therefore, if the user naturally sits on a mat, which is placed on a flat chair, with his feet on the floor, his pelvis portion is apt to be bent backwards while the pelvis portion keeps a forward-bending state in a standing posture, thereby the coccyx, the sacrum and the vertebral column also become bent backwards.
As a result, the vertebral column becomes bent backwards, losing the natural physiological curvature, and the weight of the upper body is applied to the periphery portions of the coccyx and the sacrum, the lower lumbar vetebra portion, the intervertebral discs, or the rear portions of the thighs. Accordingly, the load applied to the waist portion or the coccyx portion becomes increased.
Furthermore, the user may easily sit with his legs crossed, the weight of the upper body that is applied to the hipbone becomes unbalanced, possibly causing the deformation of skeleton.
In order to resolve the above problems, an auxiliary chair for improving sitting posture has been suggested for a chair, which is formed in the size and thickness for a user to seat thereon and includes a seating surface portion curvedly formed in a convex shape on the top portion thereof and having an indented portion 7 formed in the shape of a strip in the center in the back and forth direction, an uplifted portion 10 formed at a front portion of the seating surface portion 6 and smoothly uplifted towards the indented portion 7 at both sides of the indented portion 7, a fan-shaped inclination surface formed at the lower side of the uplifted portion 10 so as to be smoothly inclined in the forward inclination direction, a curved portion 16 formed to be convex in the center of the lower portion of the uplifted portion 10, and stopper portions 17 and 18 formed at the outer side portions of the seating surface portion 6, as shown in FIGS. 1 and 2 (Korean Patent Publication No. 10-2009-0095639).
If a user seats on a chair via the auxiliary chair (a), his legs become spread such that crossing his legs becomes difficult, the pelvis portion becomes bent forwards, and the lumbar vetebra portion is induced to be naturally bent. Therefore, the weight of the upper body that is applied to the periphery portions of the coccyx and the sacrum, the lower lumbar vetebra portion, the intervertebral discs, or the rear portions of the thighs becomes distributed to the legs in balance. Accordingly, the legs are worked out and simultaneously the load applied to the waist or the coccyx may be reduced. Further, the pelvis is prevented to be bent backwards, so that the backword bending of the lumbar vetebra for a long time may be prevented, improving the sitting posture of the user.
As described above, in the case of sitting on a chair or flat floor, if the pelvis is stably supported using an auxiliary instrument, which is indented in the center thereof like the auxiliary chair a, right sitting posture may be kept, promoting the health of the backbone.
In the meantime, in a human body, the pelvis portion indicates a large compound bone structure at the base of the spine, which is formed in the shape of a funnel at the waist portion, and consists of lumbar vertebra portion, the os coxa, the sacrum, the coccyx and the hipbone.
Furthermore, the lumbar vertebra portion is so-called as vertebrae lumbales between the thoracic vertebra and the sacrum in the vertebra, wherein a human has five mallei.
The prior art auxiliary chair a has, however, a disadvantage that the chair has not cushion materials so that the comfortable sitting cannot be expected even though the chair may support the pelvis portion so as to keep the right sitting posture. Furthermore, the prior art auxiliary chair has another disadvantage that the chair cannot support the lumbar vertebra portion, so that a load is applied to the lumbar vertebra portion after a long time sitting, thereby possibly inducing damage or pain.